1. Field of the Invention
This invention relates in general to tieback wellhead connectors for connecting to a subsea wellhead.
2. Description of the Prior Art
Subsea wells normally have a wellhead housing, which is a large tubular member located at the sea floor. Casing will be supported in the wellhead housing by a casing hanger. In one type of well, a riser will extend upward from the subsea wellhead housing to a platform. A Christmas tree will be mounted at the platform for controlling the flow of the produced fluid. A tieback wellhead connector will connect the lower end of the riser to the wellhead housing.
An external wellhead connector normally has a body that bolts to the lower end of the riser, which typically is a stress joint. The stress joint is a tubular member that is tapered for handling bending stress due to wave and current motion. Tension bolts extend through an external flange of the stress joint into the body to secure the body to the stress joint. The body has a cylindrical portion that extends around the wellhead housing. The body has a downward facing shoulder that lands on the upper rim of the wellhead housing. A seal locates at the shoulder between the wellhead housing and the wellhead connector body.
A locking element, preferably a set of dogs, will be pushed out from a retracted position into engagement with an external profile on the wellhead housing. A seal sub secures to the lower end of the stress joint and extends sealingly into the bore of the casing hanger in the wellhead housing. A flange of the seal sub is compressed between a portion of the body and the lower end of the stress joint.
The dogs are pushed into the engaged position by a cam ring. The cam ring connects to rods which extend through holes in the body up to an actuator ring. The running tool engages the actuator ring to push the cam ring downward for moving the dogs to the engaged position. For later removal of the wellhead connector, the running tool will lift the actuator ring, which in turn lifts the cam ring.
While this type of connector is workable, it would be desirable to eliminate some of the seals and to reduce the weight and number of components.